[effects/fadedesktop] Don't animate windows moved between virtual desktops
If a window was moved to another virtual desktop, then it would be faded
in. The desired behavior is to not animate it at all.
Test Plan: Moved a Konsole window between virtual desktops, it stayed opaque.
Reviewers: KWin, davidedmundson
Reviewed By: KWin, davidedmundson
Differential Revision: https://phabricator.kde.org/D16102